Controlling system for electric elevators.



W. S. SM'iTH.

CONTROLLING'SYSTEM FOR ELECTRIC ELEVATORS.

APPLICATI ON FILED MAR. 28, |91e.

1,228,075. Patented May 29, 1917.-

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WILLIAM- S. SMITH, OF CAMBRIDGE, MASSACHUSETTS.

v v CONTROLLING SYSTEM non ELECTRIC ELEVATORS.

Specification of Letters Patent.

Patented May29, 1917.

Application filed March 28, 1916. Serial No. 87,294.

ToaZZ whom it may concern:

tems for Electric Elevators, of which the following is a specification, reference being had therein to the accompanying draw ngs.

My inventlon relates to the electrical operation of elevators by the use of a pushbutton system. 7 v

The principalobject of the invention is to providea system which is highly efficient, simple in operation and of low cost both in installation and maintenance.

A further object is to secure a system in which interference with the elevator car afterit has been started by the operation of a push-button is impossible until after the car has reached its destination.

Another obj eet is to provide means whereby in case the elevator car is started by the operation of a push-button within the car all interference with the car by the operation of any push-button is prevented until after the car has reached its destination and the elevator door has been opened and closed.

Additional objects of the invention will be more specifically set forth and described hereinafter.

The preferredembodiment of my 1nvention comprises the following general fea tures. For operating the elevator car n either direction, a motor of any suitable construction is. arranged in a circuit, preferably across the line, which is closed and openedto startand to stop the motor by a reversing-switch of any suitable design. At each floor or station a push-button or other circuit-closing device is provided and when the car is employed for carrying passengers a similar series of push-buttons is installed 1n the car, the latter push-buttons corresponding in number and arrangement to those at the stations. These push-buttons, both at the stations and in the car are included in suitable circuits arranged when any one circuit is closed by the operation of a push button to set in motion means for operating the reversingswitch to start the motor. To prevent the interference with the car after it has started and before it has reached its destination which would-ensue from the operation of another push-button, means are provided for short-circuiting all of the push-button circuits until after the car has reached its destination and during the movement of the car the operation of any pushbutton is entirely without effect. In addition, means are provided whereby when a push-button in the car is operated, all of the push-buttons are short-circuited until after the car has come to rest at its destination and the station door has been opened.

Although various means may be utilized for accomplishing the foregoing results, the preferred embodimentof'the invention contemplates the employment of a. series of floor-magnets arranged in the push-button circuits and adapted to be actuated by the operation of a push-button to close a circuit which operates the reversing-switch to start the motor. Each floor-magnet has two windings or coils, one of which may be termed an actuating-coil and is included in a circuit with one of the station push-buttons and a corresponding car push-button and the other of which may be called a retaining-coil for holding the magnet in any operated position, all of the retaining-coils on all of the magnets being arranged to be energized by the operation of any one of the push-buttons. Whenever a floor-magnet is operated by the closing of a push-button circuit, means carried by the magnet operates to close a circuit for actuating the reversing-switch to start the motor. By providing the reversing-switch with circuitclo-sing means, I am enabled to short-circuit the push-buttons to prevent interference and the short-circuit is so arranged that the retaining-coils on all'the floor-magnets are included in the closed circuit which thereby retains .any operated floor-magnet in its operated position.

In systems where the car is used for carrying passengers I provide an additional magnet having likewise an operating-coil and a retaining-coil, the latter being in series with the retaining-coils on the floormagnets but the former being in series with the common conductor to the push-buttons in the car whereby interference with the elevator car is prevented until the car has reached its destination and the hoistway door has been opened. a

In the accompanying drawings, illustrating an apparatus for controlling elevators constructed and operated in accordance with my invention, is shown a diagrammatic view of the preferred arrangement of circuits and apparatus.

In the drawings the apparatus is shown as actuated by a direct current but, with proper modifications, all of which will be apparent to one familiar with the art, the system may be used in connection with an alternating current.

The illustrated embodiment of the invention contemplates a system applied to four stations or floors, but the number of stations or floors may be reduced or increased by merely subtracting from, or adding certain units to the system shown in the drawmgs.

Referring to the drawings, the positive and negative supply lines are designated as 3 and 41- respectively and 5 is the armature of a motor, shown as a shunt motor, having a field coil 6 that is connected to the supply lines by conductors 7 and 8, the circuit being controlled by a switch 9. For operating the motor the circuit is across the line through the conductors 10 and 11 the circuit being closed and opened by a reversingswitch 12 to be hereinafter described.

The operation of the motor through the reversing-switch is controlled from the various floors or stations by providing suitable circuit closing devices such as push-buttons a a a and a, located at the four floors or stations respectively and, when the elevator car is employed for carrying passengers, a similar series of push-buttons b b b and 6 is installed in the car. The hoistway doors, one on each floor, are provided with contacts 0 c 0 and 0 respectively, each contact being opened when the door is opened and closed when the door is closed; all of these contacts being included within the push-button circuits so that unless all the hoistway doors are closed, all the pushbutton circuits are open and the system is out of operation.

Arranged to be operated by the closing of the push-button circuits are a series of floor-magnets e e c and 6 corresponding in number to the number of floors or stations in the system. Each floor-magnet is provided with two windings or coils d and r; the coils (Z (Z (Z and (Z being termed actuating-coils and the coils r 1",, r and 1, called retaining-coils. The latter are wound with sufficient ampere turns to retain the magnets in any operated position but are not of suflicient strength to operate them. The actuating-coils are strong enough when excited in conjunction with the retaining-coils to operate their respective magnets. Both sets of coils are included in the push-button circuits, the retaining-coils being connected in series and energized whenever a pushbutton is operated and the actuating-coils being each included with its respective pushbutton so that the operation of a push button energizes its respective actuating coil only.

Whenever a push-button at a floor is operated, it closes a circuit from the main 3 through conductor 13, door contacts 0,, c c and c conductor 14, conductor 15, retaining-coils 1",, 1' 1, and 1",, conductor 16 to point 17, conductor 18, thence through the actuating-coil (Z corresponding to the pushbutton actuated and then through the pushbutton and conductor 19 to the negative side of the line.

If desired an adjustable resistance B may be included in the conductor 15 to permit of convenient adjustment of the current in the retaining-coils.

The magnets 6 e e, and c carry contactmembers f f f and f, respectively which are adapted when the magnets are operated to engage contacts 9 h 9 k 9 72, and 9,, h, respectively to close various control circuits through suitable conductors and switches which direct the current to the reversing-switch in such manner as to start and to stop the motor as desired. The control circuits may be divided into two groups, one to cause the car to descend and the other to affect its ascension.

In the first group of control circuits are arranged the contacts 9 h 9,, h, and g 7L3 and switches j j, and and in the second group the contacts 9 7a,, 9 k and 9,, k and switches j a, j a and 7' The switches are operated by a suitable controller or member C which moves in synchronism with the car and as shown in the drawing moves to the right when the car is ascending and to the left when it is descending.

The reversing-switch 12 which may be of any suitable design is illustrated diagrammatically in the drawing as made up of two magnets 70 and 70 each provided with necessary contacts for closing the motor circuit. The magnet 70 is included in the first group of control circuits and the magnet is, is in the second group. The former magnet carries contact-pieces 25 and 26 which, when the magnet is energized, are moved into engagement with contacts 27 and 28 and 29 and 30 respectively to close the motor circuit and to admit current to the motor in such manner as to cause the car to descend. Similar contact-pieces 32 and 33 are, by the operation of magnet k thrown into engagement with contacts 34 and 35 and 36 and 37 respectively thereby closing the motor circuit in such a way as to cause the car to ascend.

The control circuits may be arranged in any suitable manner and one such arrangement is shown in the drawings. From the positive main all of the control circuits use a common conductor comprising conductor 18, contacts 0 0 0, and 0 conductor 14 and conductor 40, and from this latter concuits are joined by connecting switches y' and j with conductor 44 by conductor 50 and from that point these circuits are completed through switch j conductor 51, coil 52, energizing magnet 10,, conductor 53 and conductor 49 to the negative main 4.

From the foregoing description it will be noted that the operation of a push-button by energizing all the retaining-coils and the actuating-coil on its respective floor-magnet causes the latter to operate and to close one of the control circuits thereby starting the motor through the reversing-switch. So

far, however, there is nothing to prevent the operation of another push-button causing a different floor-magnet to close another control circuit and thereby interfere with the operation of the motor and the progress of the car toward its destination. To obviate this difliculty, I provide means for short-circuiting all of the push-buttons whenever the reversin switch is operated to start the motor and oneform of such means is illustrated in the drawing and comprises contact-members 60 and 61 carried by magnets 71: and respectively and adapted when either magnet is operated to engage contacts 62 and 63 and contacts 64 and 65 re spectively to short-circuit the push-button circuits from point 17 through conductors 66 and 67 to the negative main 4. The result is that the operation of the reversing-switch due to the pressing of a push button immediately short-circuits all of the push-buttons until the reversing-switch has returned to its normal inoperative position after the car has reached its destination and during this time the pressing of any pushbutton has no effect.

WVhen the car reaches its destination the hoistway door at that point is opened which breaks all of the push-button circuits and circuits are short-circuiteduntil after the car 7 has reached its destination and the hoistway door at that destination has been opened. In the drawing I have shown means for accomplishing this end whenever the oar is used for carrying passengers and a car push-button has been operated. Although these means might be extended to attain the same result when a floor or station push-button is operated, yet it is inadvisable because one might operate a station push-button and call the car to thatstation and then decide not to use the car and leave without opening the hoistway door, in which case the entire system would be out of operation until that particular door was opened. This objection does not apply to the elevator car because a person within the car must open a hoistway door in order to leave the car.

For the foregoing purpose, I provide an additional magnet 6 having a retainingcoil 1", and an actuating-coil (Z similar to the floor-magnets with the exception that while the retaining-coil is in series with those on the floor-magnets the actuating-coilis in series with the common conductor 19 to the push-buttons b b b and b, in the elevator car and in consequence the magnet 6 is operated only when a car push -button is pressed. Carried by the magnet 6 is a contact-member 7, which is adapted, when the magnet is operated, to engage contacts 9 and h, and thereby complete a shortcircuit of all the push-buttons through conductor 70 from point 17 to the negative main. This short-circuit is not affected by the operation of the reversing switch and is not opened until the circuit is opened by the opening of a hoistway door.

If desired a safety button shown as s may be installed in the car. This button is included in the push-button circuit by conductor 72 and when pressed breaks the circuit thereby restoring the system to its normal inoperative condition. It enables a passenger in the car to stop the car at any point and to change its destination.

The operation of my system is as follows: In the drawing the system is shown in its normal inoperative condition and the position of C the controller indicates that the car is at the third floor. Suppose that a person at the second floor desires to call the car to that floor. He pushes the button a, for an instant and then releases the pressure. If any hoistway door is open the operation of the button produces no effect but if all the doors are closed then a circuit is completed from the positive main 3 through conductor 13, door contacts 0 0 c and c (ignoring the s but ton) conductors 14 and 15, retaining-coils r r 1",, and r conductor 16, retainingcoil 11,, conductor 18, coil (Z push-button a, and conductor 19 to the negative main 4. The closing of this circuit energizes all of the retaining-coils and the actuating-coil d, and in consequence the combined pull of the coils (Z and r is sufficient to operate the magnet 6 and causes the contact-member f,

to engage the contacts 9 and 71 This establishes another circuit from the positive main through conductor 13, door contacts, conductor 14, conductor 40, contact 9 contact-member f contact 7L conductor 42, switch 7' conductor 45, switch 7' conductor 46, coil 47, conductor 48 and conductor 49 to the negative main. The energizing of coil 47 operates the magnet is and the contact-members 25 and 26 engage the contacts 27 to 30 inclusive and closes the motor circuit through conductors 10 and 11 and admits current to the motor in such a manner that the car descends.

The operation of the magnet 70 in addi tion to admitting current to the motor also short-circuits the push-buttons to prevent interference with the car after it has started, through the engaging of contacts 62 and 63 by the contact-member 60 which establishes a short-circuit from point 17 through conductors 66 and 67 to the negative main 4. The result of this short-circuit is that all of the push-buttons, both at the floor stations and in the car are inoperative. The coil (Z2 is de'energized by this short-circuit but this does not affect the magnet 6 because the retaining-coil r, is of sufiicient strength to retain the magnet in an operative position.

The motor having started in such manner as to cause the car to descend, the member G moves with a speed relative to the speed of the car in a direction corresponding to the down direction of the car, that is, as shown in the drawing, from right to left. Moving in this direction, the member C first engages switch jga nd closes it, which, how ever, has no efi'ect since this switch is in that group of control circuits governing the car when ascending. The member C continuing its movement to the left next engages the switch j, and opens it thereby opening the control circuit which was established by the operation of the magnet 6 through contacts 9,, 72, and switch j When the control circuit is broken the magnet 70 is deenergizeol and returns to an inoperative position thereby opening the motor circuit and, in consequence, the motor comes to rest with the car at the second fioor and the member C between switches 7 2. and y' The return of the magnet to an inoperative position causes the contact-member 60 to disengage from the contacts 62 and 63 opening the short-circuit which had previously been established through conductors 66 and 67. This breaks the circuit through the retaining-coils and allows the magnet 6 to return to its normal inoperative position and the system is then in its normal condition ready to be set into operation again by the pressing of a push-button. It will be noticed that when a push-button circuit is established by the pressing of a push-button as heretofore explained, the respective floormagnet for that push-button and one of the reversing-switch magnets are simultaneously operated and the control circuit and the short-circuit around the push-buttons will be immediately established. A momentary pressure of a push-button is sufficient to accomplish this result and when the pressure is released from the push-button then that push-button circuit as well as the others are in their normal open condition, but the short-circuit established by the reversingswitch contact merely serves to prevent the push-button circuits being effectively closed by the operation of a push-button until after the car has reached its destination and the system has returned to a normal condition.

In the foregoing description of the operation of my system I have assumed that the car is being called to a certain floor by the pressing of a push-button at a floor station. When a push-button is operated in the elevator car by a person desiring to go to another floor the operation ,of my system is slightly different in so far as the short-circuiting of the push-buttons is concerned. Assuming, for instance, that the system is in the condition shown in the drawings, with the car at the third floor and a person in the car desires to go to the second floor, he pushes momentarily the button 7),. This closes a circuit from the positive main 3 through conductor 13, door contacts, conductor 14, conductor 15, all of the retainingcoils to point 17, thence through conductor 18, coil (Z push-button b conductor 74, coil d conductor and conductor 19 to the negative main 4. The closing of this current by energizing the coils 1 and (Z operates the magnet 6 to establish the control circuit hereinbefore described. At the same time the two coils a", and (Z, being energized, the magnet e, is caused to operate, thereby moving contact-member 7, into engagement with contacts 9 and h, and establishing a short-circuit from the point 17 through contact 7t, contact-member f,, contact 9, and conductor 70 to the negative side of the line. The short-circuit established by the operation of the reversing-switch through c011- ductors 66 and 67 is of no effect because this short-circuit is itself short-circuited by the circuit established through the conductor 70. From this point the operation of the system is identical with the operation heretofore described until the elevator car has reached its destination when the control circuit is broken and the motor stops. The circuit which was established by the operation of the magnet e, is still closed because this circuit is from the positive main 3 through the conductor 13, door contacts, conductor 14, conductor 15, retaining-coils r r r 1", and r contact 7L contact-member i contact 9,, conductor 70 to the negative main and this circuit remains closed until the hoistway a safety button 8 to break all the circuits and coil (Z is excited instead of coil d, and the magnet e, is operated instead of magnet e,. The operation of push-button b closes a circuit from the positive main 3, through conductor 13, door contacts, conductor 14, conductor 15, all of the retaining-coils, conductor 1S, coil (Z push-button (a, conductor 19 to the negative main. The combined pull of the coils d, and r, operates the magnet 6 causing the contact-member f, to engage contacts 9,, [L4, and establish a control circuit from the positive main through conductor 13, door contacts, conductor lt, conductor 40,

contact 9,, contact member f contact 7L4, conductor 4%, switch j conductor 51, coil 52, conductor 53 and conductor 49 to the negative main 4. This circuit operates the magnet 70, and admits current to the motor in sucha way as to cause the'car to ascend.

The energizing of the coil 52 by the closing of this control circuit causes the magnet is, of the reversing-switch to operate and thereby the contact-member 61 carried by that magnet is brought into engagement with contacts 6 1 and 65 and closes a shortcircuit from point 17 through conductors 66 and 67 to the negative main cutting out all of the push-buttons and rendering their operation ineffective; the retaining coil 9, not being short-circuited by this operation still continues'efiective to main the magnet 6 in its operated position with the control circuit closed.

As the car starts to ascend from the second floor the member C moves to the right, referring to the drawings, first closing switch 7' which produces no effect as this switch is in the group of control circuits governing the descent of the car. Continuing its movement the member C next reaches switch j,, and opens it, still without effect, however, as

net 74 to return to an inoperative position and the motor to stop with the car at its destination, the fourth floor. The return of the magnet is, to normal position breaks the short-circuit established through the conductors 66 and 67 and magnet 6, drops into an inoperative position and the system is then in normal condition ready to be throwninto operation by the pressing of a push-button.

This last description covers the operation of the system when the car is called to the fourth floor by the pressing of the push-button at the fourth floor station. In case, however, the push-button b, in the car is pressed by a passenger in the car who desires to go to the fourth floor, the operation is modified in the same manner as previously described when the push-button b, was pressed to take the car to the second floor; that is, the magnet 0 is operated to establish a short-circuit through the conductor 70 which circuit remains closed after the motor stops and until the hoistway door is opened.

From the foregoing description it will be observed that my system is of great simplicity both in construction and in operation and, therefore, combines great efficiency with low cost of installation and maintenance.

It will also be apparent that it may be applied to any number of floors or units by merely adding suitable members and suitable connections.

It is further to be understood that my invention may be embodied in various other forms of construction than that herein shown and described and except where specifically limited in the following claims it is my desire to claim the invention broadly.

What I claim is 1. In an apparatus for controlling elevators the combination with a motor, a car and a plurality of stations of motor-controlling devices, means for operating said devices from said stations, means for retaining said operating means whenever actuated in an operative position and means for shortcircuiting said stations and said means for operating said motor-controlling devices to exclude control of said operating means from said stations until the car has reached its destination.

2. In an apparatus for controlling elevators the combination with a motor, a car and a plurality of stations of motor-controlling devices, fioor-magnets corresponding in number to the number of said stations for operating said devices, means for actuating said floor-magnets from said stations, means for retaining said floor-magnets in actuated position and means for short-circuiting said stations and said actuating means to exclude control of said motor-controlling devices from said stations until the car has reached its destination.-

3. In an apparatus for controlling elevators, the combination with a motor, a car and a plurality of stations of motor-controlling devices, means for operating said devices from said stations, means for retaining said operating means whenever actuated in an operative position and means for shortcircuiting said station and said operating means to exclude control of said operating means from said stations until after the car has reached its destination and a door has been opened.

l. In an apparatus for controlling elevators, the combination with a motor, a car and a plurality of stations of motor-controlling devices, floor-magnets corresponding in number to the number of said stations for operating said devices, means for actuating said floor-magnets from said stations, means for retaining said floor-magnets in actuated position and means for short-circuiting said stations and said means to exclude control of said floor-magnets from said stations until after the car has reached its destination and a door has been opened.

5. In an apparatus for controlling elevators, the combination with a motor, a car and a plurality of stations of motor-controlling devices, floor-magnets corresponding in number to the number of said stations for operating said motor -controlling devices, means for actuating said floor-magnets from said stations and from said car, means for retaining said floor-magnets in actuated position and means for short-circuiting said stations, said car and said actuating means to exclude control of said floor-magnet from said stations and said car until after the car has reached its destination and a door has been opened.

6. In an apparatus for controlling elevators, the combination with a motor of pushbuttons for each floor or station, push-buttons in the car corresponding to the pushbuttons on each floor or station, suitable circuits and connections including the pushbuttons, means operated by said circuits to Start the motor and means for short-circuiting the push-button circuits until after the car has come to rest and a door has been opened, means for maintaining the short-circuit on the push-buttons after the car has come to rest until after the door contacting circuit has been opened.

7. In an apparatus for controlling elevators, the combination with a motor for oper ating the car in either direction of a reversing-switch, a push-button for each floor or station, push-buttons in the car corresponding in number and arrangement to the various floors, a magnet for each floor, each floor-magnet being provided with an actuating-coil and with a retaining-coil, both of said coils being in circuit with the push-buttons at the floor stations and in the car, means whereby the operation of the floormagnet operates the reversing-switch to start the motor and means for short-circuiting all of the push-buttons until after the car has reached its destination and the door has been opened.

8. In an apparatus for controlling elevators, the combination with a motor for operating the car in either direction of a reversing-switch, a push-button for each floor or station, push-buttons in the car corresponding in number to the push-buttons for said floors or stations, floor-magnets corresponding in number to the number of push-buttons at the stations and in the car, each floor-magnet being provided with an actuating-coil and a retaining-coil, the actuatingcoil of each of said floor-magnets being in circuit with its respective push-button, bothat the station and in the car, means actuated by the operation of any one of said fioormagnets for operating said reversing-switch to close the motor and automatic means 101' short-circuiting all of said push-button circuits whenever the reversing-switch is actuated to operate said motor.

9. In an apparatus for controlling elevators, the combination of a motor for operating the car in either direction, a reversing-switch, a floor-magnet for each floor or station, each floor-magnet having an actuating-coil and a retaining-coil, a push-button for each floor or station, suitable circuits whereby the operation of a push-button closes a circuit through the actuating-coil and the retaining-coil of its respective floormagnet, means whereby the operation of a floor-magnet operates the reversing-switch to start the motor and means for short-circuiting the said circuits including the pushbuttons and the actuating-coils on said floormagnets until the car has reached its destination.

10. In an apparatus for controlling elevators, the combination of a motor for operating the car in either direction, a reversingswitch, a floor-magnet for each floor or station, each floor-magnet having an actuatingcoil and a retaining-coil, a push-button for each floor or station, suitable circuits whereby the operation of a push-button closes a circuit through the actuating-coil of its respective floor-magnet and through the retaining-coils of all the floor-magnets, means whereby the operation of a floor-magnet 0perates the reversing-switch to start the motor and means for short-circuiting the said circuits including the push-buttons and the actuating-coil on said floor-magnets until the car has reached its destination.

11. In an apparatus for controlling elevators, the combination of a motor for operating the car in either direction, a reversing-switch, a floor-magnet for each floor or station, each floor-magnet having an actuating-coil for operating it and a retaining-coil for retaining it in any operated position, a push-button for each floor or station, suitable circuits whereby the operation of a push-button closes a circuit through the actuating-coil and the retaining-coil of its respective floor-magnet, means whereby the operation of a floor-magnet operates the reversing-switch to start the motor and means for short-circuiting the said circuits including the push-buttons and the actuating-coils on said floor-magnets until the car has reached its destination.

12. In an apparatus for controlling elevators, the combination of a motor for operating the car in either direction, a reversingswitch, a circuit for operating the reversingswitch, a floor-magnet for each floor or station, each floor-magnet having an actuatingcoil and a retaining-coil, a push-button for each floor or station, suitable circuits whereby the operation of a push-button closes a circuit through the actuating-coil and the retaining-coil of its respective magnet, means operated by the said floor-magnets when energized for closing said reversingswitch circuit to start the motor and means for short-circuiting the said circuits including the push-buttons and theactuating-coils on said floor-magnets until the car has reached its destination.

18. In an apparatus for controlling elevators, the combination of a motor for operating the car in either direction, a reversing switch, a magnet for operating said reversing-switch to start the motor, a circuit for energizing said magnet, a floor-magnet for each floor or station, each floor magnet having an actuating-coil and a retaining-coil, a push-button for each floor or station, suitable circuits whereby the operation of a push-button closes a circuit through the actuatingcoil and the retaining-coil of its respective floor-magnet, means whereby the circuit for energizing said reversing-switch magnet is closed whenever a floor-magnet is operated by a push-button and means for short-circuiting the said circuit including the pushbuttons and the actuating-coils on said floormagnets until the car has reached its destination.

14:. In an apparatus for controlling elevators, the combination of a motor for operating the car in either direction, a reversingswitch, a floor-magnet for each floor or station, each floor-magnet having an actuating-- coil and a retaining-coil, a push-button for each floor or station, suitable ,circuits whereby the operation of a push-button closes a circuit through the actuating-coil and the retaining-coil of its respective floor-magnet, means whereby the operation of a floor-magnet operates the reversing-switch to start the motor and means for short-circuiting simultaneously all of the said circuits including the push-buttons and the actuating-coils on said floor-magnets until the car hasreached its destination.

In testimony whereof, I hereunto set my hand this twentieth day of March, 1916.

WVILLIAM S. SMITH.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. C. 

